In manufacturing processes for various glass products, a glass raw material, which has been formulated and mixed, is melted, and the glass in the molten state is stirred to homogenize its component and uniformize the index of refraction, and then, is formed to obtain a glass product. There has been a demand for glass products having uniform quality and free from defect (striae, bubbles, and so on), and in such situation, the stirring process is particularly important in these glass manufacturing processes.
In general, the stirring process for molten glass is performed by inserting a stirrer for manufacturing glass into a molten glass tank, and rotating it. This stirrer for manufacturing glass is configured such that a stirrer shaft (hereinafter, also simply referred to as a shaft) serving as a rotating shaft is provided with a stirrer blade (hereinafter, also simply referred to as a blade). There are some known modes of the shape of a blade provided to the shaft. For example, these known modes include one having plural rod-shaped bodies serving as blades and protrudingly joined to the shaft in a multi-stage manner as illustrated in FIG. 5 (see PTL 1), one having a plate material joined spirally around the outer periphery of the shaft as illustrated in FIG. 6 (see PTL 2), and one having a flange-shaped protruding portion formed spirally around the outer periphery of the shaft as illustrated in FIG. 7. These different types of stirrers are used depending on shape or size of the stirring tank, or properties or quality required for molten glass to be processed.